Lubricants inhibited against oxidation



United States Patent 3,184,412 LUBRICANTS INHIBITED AGAINST OXIDATION Warren Lowe, Berkeley, and Frank A. Stuart, Orinda,

(Ialih, assignors to California Research Corporation, F San Francisco, Calif., a corporation of Delaware No Drawing. Filed Sept. 28, 1962, Ser. No. 227,037 4 Claims. (Cl. 25246.7)

This invention pertains to lubricating oil compositions having incorporated therein metal-free detergents. These particular detergents are also efiiective as oxidation inhibitors.

Present day internal combustion engines operate at high speeds and high compression ratios. when used in the so-called city stop-and-go driving, which includes the greater part of the driving conditions for a large percentage of todays automobiles, the internal combustion engines do not reach the most eflicient operating temperature. Under city driving conditions, large amounts of partial oxidation products are formed, and reach the crankcase of the engine by blowing past the piston rings. Most of the partial oxidation products are oil-insoluble, tending to form deposits on the various operating parts of the engine, such as the pistons, piston rings, etc. For the purpose of preventing the deposition of these products on the various engine parts, it is necessary to incorporate detergents in the lubricating oil compositions, thus keeping these polymeric products dispersed in a condition unfavorable for deposition on metals.

For the most part, the detergents which are added to crankcase oils to reduce this formation of sludges and varnishes are metal organic compounds, particularly those compounds wherein the metal is linked to an organic group through an oxygen atom. Although these metal-containing organic compounds have some effec- 35 tiveness as detergents for dispersing the precursors of the deposits within the oil itself rather than permitting them to form as deposits on the engine parts, they have the disadvantage of forming ash deposits in the engine. These ash deposits lower engine performance by fouling spark plugs and valves, and contributing to pre-ignition.

It is a particular object of this invention to provide lubricating oil composition having incorporated therein metal-free detergents which are also effective as oxidation inhibitors. Thus, these new additives inhibit the oxidation of lubricating oil compositions and also disperse the undesirable polymeric products which are formed.

Therefore, in accordance with this invention, it has been found that lubricating oil compositions particularly useful for heavy duty service are obtained by incorporating therein a product obtained by reacting an alkenyl succinic anhydride and a piperazine derivative, followed by reaction with a dihydrocarbyl dithiophosphoric acid to form a salt thereof.

By the use of lubricating oil compositions containing the salts described herein, diesel and gasoline engine products remain remarkably free of deposits and varnish even under severe operating conditions.

The alkenyl succinic anhydrides which are reactants herein are of the formula R-CH-C wherein R is a hydrocarbon radical having from 10 to 200 carbon atoms therein, preferably 50 to 200 carbon atoms. Examples of alkenyl radicals include n-decenyl,

'ice

n-hexadecenyl, propylene tetramer, butylene trimer, porpylene polymers containing from 50 to 200 carbon atoms, and polymers of mixtures of l-butene and isobutene having from 50 to 200 carbon atoms.

The piperazine derivatives, which contribute the imide and the basic nitrogen atoms of the recation products herein, are represented by the formula era-0H,

NR3 GE -C wherein the R represents a divalent alkylene radical having from 1 to 3 carbon atoms, and R is hydrogen or an alkyl radical having 1 to 3 carbon atoms. R is exemplified by the methylene radical, the ethylene radical, and the propylene radical. R is exemplified by hydrogen, the methyl radical, the ethyl radical, the n-propyl radical, the isopropyl radical, etc.

The dihydroearbyl dithiophosphoric acids which are used in the salt formation herein are represented by the formula wherein R and R represent hydrocarbon radicals each having from 1 to carbon atoms, preferably from 4 to 20 carbon atoms. The R nd R combined can have a total of from 6 to 50 carbon atoms, preferably from 10 to carbon atoms.

The R and R radicals are exemplified as follows: methyl, ethyl, propyl, isopropyl, etc.

Examples of dihydrocarbyl dithiophosphoric acid include dimethyldithiophosphoric acid, methylethyldithiophosphoric acid, diethyldithiophosphoric acid, di-n-propyl dithiophosphoric acid, di-isopropyldithiophosphoric acid, di-n-butyldithiophosphoric acid, diisobutyldithiophosphoric acid, n-butyl-n-amyldithiophosphoric acid, disec amyldithiophosphoric acid, methyl-n-hexyldithiophosphoric acid, isobutyl-n-hexyldithiophosphoric acid, di-noctyldithiophosphoric acid, methylcyclohexyl dithiophosphoric acid, methylcyclohexyldithiophosphoric acid, dicyclohexyldithiophosphoric acid, methylphenyldithiophosphoric acid, diphenyldithiophosphoric acid, di- (amylphenyl) dithiophosphoric acid, di- (hexadecylphenyl)dithiophosphoric acid, etc.

The reaction between a piperazine derivative and an alkenyl succinic anhydride can proceed at temperatures ranging from 220 F. to 500 F., preferably from 220 F. to 350 F.

The mol ratio of piperazine derivatives to succinic anhydride can vary from 0.5 :1 to 1:1. Preferably, the polyamine-anhydride mol ratio is 0.95:1.

For purposes of simplicity, the product obtained by the reaction of the piperazine derivative and an alkenyl succinic anhydride will be termed a succinimide.

The succinimides herein are reacted with a dihydrocarbyl dithiophosphoric acid at temperatures insufiicient for hydrogen sulfide formation; such temperatures being from F. to 220 F., preferably F. to 200 F.

The mol ratio of the succinimide to the dihydrocarbyl dithiophosphoric acid can vary from 1:1 to 1:4. Preferably, the mol ratio is 1:1.

As identified herein, the term salt means the product obtained by reacting the above-identified succinimide with the described dihydrocarbyl dithiophosphoric acid.

Lubricating oils which can be used as base oils include a wide variety of lubricating oils, such as naphthenic base, paraflin base, and mixed base lubricating oils, other hydrocarbon lubricants, e.g., lubricating oils derived from coal products, and synthetic oils, e.g., alkylene polymers (such as polymers of propylene, butylene, etc., and the mixtures thereof), alkylene oxide-type polymers (e.g., propylene oxide polymers) and derivatives, including alkylene oxide polymers prepared by polymerizing the alkylene oxide in the presence of water or alcohols, e.g., ethyl alcohol, dicarboxylic acid esters (such as those which are prepared by esterifying such dicarboxylic acids as adipic acid, azelaic acid, suberic acid, sebacic acid, alkanol succinic acid, fumaric acid, maleic acid, etc., with alcohols such as butyl alcohol, hexyl alcohol, Z-ethylhexyl alcohol, dodecyl alcohol, etc.), liquid esters of acids of phosphorus, alkyl benzenes (e.g., monoalkyl benzene) such as dodecyl benzene, tetradecyl benzene, etc., and dialkyl' benzenes (e.g., n-nonyl 2-ethyl hexyl benzene); polyphenyls (e.g., biphenyls and terphanyls), alkyl biphenyl ethers, compounds of silicon (e.g., tetraethyl silicate, tetraisopropyl silicates, tetra(4- methyl-2-tetraethyl) silicate, hexyl(4-methyl-2-pentoxy) disiloxane, poly(methyl) siloxane, poly(methylphenyl) .siloxane, etc. Synthetic oils of the alkylene oxide-type polymers which may be used include those exemplified by the alkylene oxide polymers.

The above base oils may be used individually or in combinations. thereof, Wherever miscible or wherever made so by the use of mutual solvents.

The succinimide-dithiophosphoric acid salt can be used in oils of lubricating viscosity in amounts of 0.10% to 40%, by weight, preferably 0.1% to 15%, by weight, more preferably 1% to 10%.

Thus, the lubricating oil compositions herein contain products obtained by (1) reacting a piperazine derivative with an alkenyl succinic anhydride, followed by (2) reacting the product of (1) with a hydrocarbyl dithiophosphoric acid.

The reaction of an alkenyl succinimide with a piperazine derivative is illustrated in the following example.

EXAMPLE I Reaction product of N-ethylpiperazine and polybutenyl succinic anhydride A mixture of 18 grams (0.14 mol) of N-(B-aminoethyl) piperazine and 200 grams (0.127 mol) of a polybutenyl succinic anhydride wherein the polybutenyl radical was derived from a polyisobutene having about 66 carbon atoms, was blended with agitation at 125 F. in a nitrogen atmosphere. The temperature was increased to 500 F. during a period of one hour, after which the absolute pressure was reduced to about 200 mm. Hg during a period of 30 minutes to facilitate the removal of water and unreacted piperazine. The reaction mixture was then allowed to reach room temperature at this reduced pressure. The reaction product contained 2.59% by weight of nitrogen.

Example II illustrates the reaction of a succinimide and a dithiophosphoric acid.

EXAMPLE II Reaction product a polybutenyl succinimide of B- aminoethyl piperazine and a dialkylphenyl dithiophosphoric acid A mixture of 1140 grams (0.5 mol) of a lubricating oil solution of a polybutenyl succinimide of Z-aminoethyl piperazine and 510 grams (0.5 mol) of a lubricating oil solution of a di(alkylphenyl) dithiophosphoric acid was vigorously stirred on a steam plate for two hours at 180 F. to 200 F., wherein said alkyl radical was a propylene polymer containing 12 to 14 carbon atoms.

Table I presents data obtained with lubricating oil compositions in the L-38 Strip Corrosion Tests, using lead strips. The numbers represent the weight loss in milligrams.

The increase in viscosity figures represent the percentage increase in viscosity at 100 F. in the oxidation stability test wherein the oil is heated at 340 F. for 20.

bon atoms, and the second alkyl radical contained 6 carbon atoms.

TABLE I L-38 test Viscosity Composition result weight increase,

loss (mgrus) percent 1. Base oil plus 2.1% weight additive A-" 1, 747 640 2. Base oil plus 3.1% weight additive B 22 11 3. Base oil plus 3.1% weight additive O--. 20 3 We claim:

1. A lubricating oil composition comprising a major proportion of an oil of lubricating viscosity and from 0.1% to 40% by weight of a product obtained by (1) reacting an alkenyl succinic anhydride having from to 200 carbon atoms in the alkenyl radical witha piperazine derivative of the formula terra ns wherein R is a divalent radical having from 1 to 3 car bon atoms and R is selected from the group consisting of hydrogen and alkyl radicals having from 1 to 3 carbon atoms, wherein the piperazine-anhydride mol ratio is from 0.5 :1 to 1:1, followed by (2) reacting the product of (1) with a dihydrocarbyl dithiophosphoric acid of the formula wherein R andR are hydrocarbon radicals each having from 4 to 20 carbon atoms and having a combined number of carbon atoms from 10 to 40, wherein the mol ratio of the product of (1) to dithiophosphoric acid is from 1:1 to 1:4, said reaction (1) being carried out by heating at a temperature from about 220 F. to about 500 F., and said reaction (2) being carried out by heating at a temperature from about F. to about 200 F.

2. A lubricating oil composition according to claim 1 in which the dihydrocarbyl dithiophosphoric acid is alkylphenyl dithiophosphoric acid.

3. A lubricating oil composition according to claim 1 in which the dihydrocarbyl' dithiophosphoric acid is dialkyl dithiophosphoric acid.

4. A lubricating oil composition comprising a major proportion of an oil of lubricating viscosity and from 0.1% to 40% by weight of a product obtained by (1) reacting an alkenyl succinic anhydride having from 50 to 200 carbon atoms in the alkenyl radical with N-(fi-amind ethyl piperazine), wherein the piperazine-anhydride mole ratio is from 0.5:1 to 1:1, followed by (2) reacting the 5 6 product of (1) with a dihydrocarbyl dithiophosphoric References Cited by the Examiner Of the frmula S UNITED STATES PATENTS l 2,809,934 10/57 Alford et a1 25232.7 5 2,973,323 2/61 Millikan et a1. 25232.7 I 2,995,568 8/61 MalZ et al. 260326.5 R 3,018,247 1/62 Anderson et a1. 25232.7 wherein R and R are hydrocarbon radicals each having 3024237 3/62 Drummond et a1 25 2 5 from 4 to 20 carbon atoms and having a combined num- 3,058,910 10/62 Culmer 252 32-7 ber of carbon atoms from 10 to 40, wherein the mole 10 3,074,990 1/63 Cyba 252 32'7 ratio of the product of (1) to dithiophosphoric acid is from 1:1 to 1:4, said reaction (1) being carried out by DANIEL WYMANPrlmary Examiner heating at a temperature from about 220 F. to about ALPHONSO D. SULLIVAN, Examiner. 500 F. and said reaction (2) being carried out by heating at a temperature from about 150 F. to about 200 F. 5 

1. A LUBRICATING OIL COMPOSITION COMPRISING A MAJOR PROPORTION OF AN OIL OF LUBRICATING VISCOSITY AND FROM 0.1% TO 40% BY WEIGHT OF A PRODUCT OBTAINED BY (1) REACTING AN ALKENYL SUCCINIC ANHYDRIDE HAVING FROM 50 TO 200 CARBON ATOMS IN THE ALKENYL RADICAL WITH A PIPERAZINE DERIVATIVE OF THE FORMULA 